In operations that use coal for fuel, finely-ground coal particles or “fines” are required for efficient operation, yielding higher combustion efficiency than stoker firing, as well as rapid response to load changes. Using coal fines for combustion also produces less nitrous oxide (NOX) emissions and keeps oversized loss-on-ignition (LOI) unburned coal particles from contaminating the marketable ash byproduct of the combustion chamber. Thus, it is common practice to supply raw coal to a device, such as a pulverizer, that will reduce the size of the coal to particles within a desirable range prior to being used for combustion.
Many pulverizers employ systems and methods including one or more crushing and grinding stages for breaking up the raw coal. For example, in a rotary pulverizer, the coal particles are reduced to dust fine enough to become airborne in an air stream swept through the pulverizer by a gradual process that includes crushing the coal by repeated crushing actions of swing hammers and grinding the coal by attrition caused by rotating elements. The dust particles are entrained in the air stream and carried out for combustion.
It should be readily apparent that the process of reducing solid coal to acceptably sized fines requires equipment and components of high strength and durability. Therefore, there exists a continuing need for components that can reduce solid coal to acceptably sized fines and yield greater overall efficiency by withstanding extremely harsh conditions and causing less operation downtime due to maintenance and repairs.
A particular type of pulverizer for size reducing solid material such as, for example, coal, comprises a raw coal inlet, a crusher dryer section, a pulverizing section, a fan section, and pulverized coal outlet. The crusher dryer section includes a plurality of beater blades all commonly mounted on a main horizontal shaft of the pulverizer, the beater blades cooperating with a grid section to effect an initial size reduction of the raw coal introduced into the pulverizer via the raw coal inlet. The pulverizing section includes a rotor disc also mounted on the main horizontal shaft for rotation thereby and a plurality of wear plate mounted on both respective axial surfaces of the rotor disc.
As the solid material is subjected to the pulverization by the pulverizing section, particles thereof cause wear and pitting of the wear plate. In addition, the particles migrate through the gaps between adjacent wear plates. These particles then cause wear and pitting of the underlying rotor disc including grooving of the rotor disc. Such wear and pitting of the rotor disc must then be remedied by removing the wear plates and costly resurfacing of the rotor disc or may even necessitate the replacement of the rotor disc before its hoped-for useful life.
However, existing technology uses wear plates that are difficult to assemble. In order to assemble the wear plates and wear components (e.g., grinding and impeller clips) to the rotor disc that make up the pulverizing section, a single person must hold together up to five individual parts, and then secure these parts with loose nuts, bolts and washers. Furthermore, existing technology uses wear components with a single wear surface, and once this single wear surface is worn, the wear component must be replaced.
Accordingly, the need still exists for an approach to controlling or limiting the migration of pulverized material through the gaps of the wear plates so as to thereby minimize wear and pitting on the underlying rotor disc. In addition, a need exists for extending component wear life, simplifying the assembly of wear plates and improving end product quality. Such an approach should preferably be inexpensive to manufacture and should be as compatible as possible with existing wear plate and rotor disc arrangements so as to facilitate the installation and use thereof. Also, the approach should be suitable for use in the relatively harsh environment of a coal pulverizing operation including being subjected to the abrasive effects of coal. The system also should be simple and reliable, in order to keep maintenance costs to a minimum.